title: Low-temperature control of nanoscale morphology for high performance polymer photovoltaics.
abstract: Understanding and controlling nanoscale morphology is crucial to the performance of polymer bulk heterojunction solar cells, as well as other optoelectronic devices such as polymer light-emitting diodes, field-effect transistors, and sensors. In photovoltaic devices, optimum blend morphologies must be commensurate with the nanometer length scales of exciton diffusion and charge separation. We report on a generally applicable method of optimizing the phase segregation in polymer-polymer bulk heterojunctions based on tuning mixtures of low and high boiling point solvents. We have characterized the resulting blend morphologies with nanometer resolution using a transient absorption technique that probes the distribution of paths traveled by the excitons themselves prior to generating charges at an interface. Photovoltaic efficiencies are accounted for in terms of exciton diffusion, geminate pair separation, and polymer ordering, all of which are sensitive to the nanoscale morphology determined by the composition of the solvent mixture.
authors.affiliation: Optoelectronics Group, Cavendish Laboratory, Department of Physics, University of Cambridge, CB3 0HE, UK.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Campbell
authors.forename: Justin M
authors.initials: JM
authors.lastname: Hodgkiss
authors.forename: Sebastian
authors.initials: S
authors.lastname: Westenhoff
authors.forename: Ian A
authors.initials: IA
authors.lastname: Howard
authors.forename: Robert A
authors.initials: RA
authors.lastname: Marsh
authors.forename: Christopher R
authors.initials: CR
authors.lastname: McNeill
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend
authors.forename: Neil C
authors.initials: NC
authors.lastname: Greenham
mesh_terms: D004563:Electrochemistry; D049329:Nanostructures / Q000737:chemistry*; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry*; D013696:Temperature
chemical_list: D011108:Polymers